Speed control system



Feb. 28, 1939. 'A, P. DAVIS ET AL SPEED CONTROL SYSTEM 2 SheetsSheet 1Filed March 18, 1937 Feb. 28, 191 39. A. P. DAVIS ET AL SPEED CONTROLSYSTEM Filed March 18, 1937 2 Sheets-Sheet 2 Illlllll E l/1,: J7

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Patented Feb. 28, 1939 UNITED STATES SPEED CONTROL SYSTEM Arthur 1.Davis, New York, and George Agins, Brooklyn, N. Y.,' assignors to ArmaEngineering (70., Inc.,' Brooklyn, N. Y., a corporation of New YorkApplication March 18, 1937, Serial No. 131,568

3 Claims. (01. 171-222) This invention relates to control systems andhas particular reference to controls for electric motors.

In accordance with this invention, a control system for electric motors,either direct or alternating current, is provided, by means of which themotor may be started, smoothly accelerated and kept running at aconstant predetermined set speed, which speed, however, can bequickly 1) changed and accurately controlled to any value within thelimits of the equipment. The direction of rotation of the motor may beselected at will upon starting and can be quickly reversed at any time.Also, the motor can be quickly stopped.

The invention comprises essentially a sensitive switching device havingreversing contacts connected in the power supply of the motor; to becontrolled, and constantly regulated jointly by a manually adjustedforce and the force applied by the motor after starting. The manuallyadjusted force, adjusted in accordance with calibrated speed values,opposes the force applied by the motor until a balance is reached whichis determined by the degree of the manual force, preselected.inaccordance with the speed desired for the motor. Any variation from thisbalance results in operation of the switch to provide thepowerconditions necessary to restore such balance. With thisarrangement, any change in the manually-adjusted force results in animmediate change in the operation of the motor untilthe aforementionedbalance is restored under the adjusted conditions, thus permitting achange in speed for the motor from one constant rate to another, as wellas rapid reversal of the motor by reversing the contacts of the switch.

For a more complete understanding of the invention, reference may be hadtothe accompanying drawings, in which:

Figure 1 is a schematic diagram of the control system of this inventionapplied to a three-phase wound rotor type motor to be controlled;

Fig. 2 illustrates schematically a modification of the arrangement ofFig. 1; and

Fig. 3 illustrates schematically an arrangement of the system adapted toa direct current or series alternating current motor.

Referring to Fig. 1 of the drawings,. numeral ID designates the motor tobe controlled, which is here shown as an induction motor of the woundrotor type, the'rotor being designated II and the stator I2. One windingI21 of the stator I2 is connected to one phase I31 of the three-phaseservice line I3. Another winding I22 of the stator I2 is connected tocontact I4 of the moving contactor I5 of a form of reversing switch I6.The third winding I23 of stator I2 is connected to the other contact Hof the moving contactor I5. A split phase condenser I8 is connectedacross stator windings I22 and I23. a

The moving contactor I5 of the switch I6 is pivoted at I9 foroscillating movement between the two sets of fixed contacts. Theopposite contacts I4 and ll of the contactor I5 are insulated from thecontactor and from each other. Moving contact I4 may engage fixedcontact and moving contact Il may engage fixed contact 2|, when thecontactor I5 is moved in a clockwise direction. When contactor I5 ismoved in a counterclockwise direction, contact I4 may engage fixedcontact 22 and contact I! may engage fixed contact 23. Contacts 2I and22 are preferably spring-mounted as shown, and a slightly smaller airgap is provided between contacts I4, 22 and I1, 2I than between contactsI4, 20 and I1, 23, for purposes to be described.

The various contacts of the switch I6 are connected between theremaining phases I 32 and I33 of three-phase service line I3. Phase I32is directly connected to fixed contacts 20 and 23. The third phase I33is directly connected to the fixed contacts 2I and 22. Condensers 24 and25 connected across cooperating contacts of the switch I6 are forsuppression of arcing between them.

The moving contactor I5 of switch I6 is provided with a lateral arm 26,the end of which engages in a fork 27 on the end of a toothed sector 28pivoted at 29. Secured to the sector 28 is a pin 39, to which areconnected the inner ends of the two coil springs and 32, the outer endsof which are connected to a suitable carriage 33 supported on the end ofa rotatable shaft 34 in such a way that the shaft may rotate relativelyto carriage 33. The other end of shaft 34 is provided with a crank 35and with a screw 36 threaded through a fixed plate 3?. A suitable dial33 mounted on shaft 34 is calibrated for motor speed and cooperates withfixed pointer 39; It will be observed that rotation of the crank 35causes up or down movement of frame 33, as seen in Fig. 1, and that thismovement is imparted through springs 3i and 32 to the sector 28, whichpivots about pin 29, operating the contactor I5 of switch I6.

A pinion 4B meshing with toothed sector 28 is connected by bevel gear Mto one side of a mechanical differential 42. The other side ofdifferential 42 is connected by gear 43 to the rotor I! of controlledmotor Ill, which has suitable resistances 44 connected across its 'rotorwindings to obtain high torque at all speeds. The shaft 45 ofdifferential 42 is provided with a flywheel 46 will move carriage 33downwardly, as seen in Fig.

1, elongating spring 32 and allowing spring 3| to compress, so thatsector 28 is rotated in a counterclockwise direction about pin 29,imparting its movement to contactor I5, which is rotated in a clockwisedirection to cause its contact IT to engage stationary contact 2| beforecontact I4 engages contact 20, owing to the different spacing.Engagement of contacts I1 and 2| results in the application of reducedtorque voltage to stator I2 of motor I0, through the action of splitphase condenser I8, so that the rotor I begins to turn. If the movementimparted to sector 28 results in further turning of contactor I5, thespring of engaged contact2| compresses, allowing further movement of thecontactor I5, so that contact I4 engages fixed contact 20, applying-fullvoltage to all three phases of motor I0. As the rotor II of motor Illturns, gear 43, which is connected to the rotor II, rotates the upperand center gears of differential 42, connected shaft 45, flywheel 46 anddisc 41.

The retarding torque, produced by the reaction of the disc 41 revolvingin the magnetic fields of the magnets 48, is proportional to the speedof the disc 41. Motor I will accelerate until it reaches thepredetermined speed, where the retarding torque acting on disc-41becomes equal and opposed to the torque produced by the restoring forceof springs 3| and 32. The center gearsof the differential 42 accordinglyroll around on the outer gears, and no movement is imparted to gear 4|or sector 28. I

However, the motor |0 continues to accelerate until it is runningslightly faster than the selected speed, whereupon the retarding torqueacting on disc 41 will become greater than the re storing force ofsprings 3| and 32. The rate of rotation of the center gears ofdifferential 20 is accordingly reduced, causing rotation of the lowergear thereof and of gear 4| and pinion 40,

with the result that sector 28 is turned about its pivot.29 in a.clockwise direction, i. e., opposite to its original movement by handcrank 35.

This movement of sector 28 results in separation of moving contact I6from fixed contact 20, opening one of the lines to the motor l0 andrestoring split phase operation thereof, which causes the motor to slowdown and results in a decrease in the retarding torque acting on disc.

41. The braking action on the differential by disc 41 is thus relieved,resulting in rotation of the sector 28 in a counterclockwise directionand reclosing of contacts I4 and 20, contacts I1 and 2| meanwhileremaining closed because of the close spacing. between them andresilient support of the latter. The motor II] again operates at fullvoltage and accelerates until it exceeds the preselected speed,whereupon the same sequence of operations is repeated. Thus, the motorspeed at the preselected rate is accurately maintained within narrowlimits.

Acceleration of the motor I0 is also governed by flywheel 46. Thus, whenthe motor starts, the inertia of flywheel 46 acts as a retarding forcewhich is greater than the restoring force of springs 3| and 32 and actsthrough the differential 42 and switch I6 to cause the contacts of thelatter to open and close intermittently, resulting in a change in themotor speed at a rate determined by the momentof inertia of the flywheel46. Although the flywheel 46 has a comparatively small moment ofinertia, its position, as shown in Fig. l, renders it as effective as aflywheel of large moment of inertia mounted in the usual positiondirectly on the shaft of motor I0.

For securing rotation of the motor ID in the 1 opposite direction, crankhandle 35 may be turned from zero speed position to any speed positionin a clockwise direction, resulting in the elongation of spring 3| andshortening of spring 32. Sector 28 then turns in a clockwise directionabout pivot 29, and contactor l5 of switch l6 rotates in acounterclockwise direction, closing contacts Id, 22 and I1, 23, theformer set closing first for initial split phase operation, becausecontact 22 is spaced nearer the contactor I5 than is contact 23. Thisreversal of switch I6 contacts reverses the phase sequence of theconnection of service line I3 to the stator I2 windings and causes motorHi to run in the opposite direction, the speed thereof beingautomatically-regulated as before described. 4

Where it is desired to rapidly reverse the direction of rotation of themotor ID from one selected speed to the same or another speed, the crankhandle 35 is rapidly turned to indicate that speed on dial 38, and thesprings 3| and 32 will thereby aid pinion 40 and sector 28 in reversingthe position of contactor I5. Assuming that in these circumstances,contact I4, 2|] and I1, 2I are closed, the former open first and thelatter next, disconnecting motor In from the power line I3. However,contacts I4, 22 immediately close, followed by closing of contacts I1,23, thus reversing the phase sequence to motor I0, which will brake themotor until it stops and, this reverses its direction of rotation. Itaccelerates to a speed slightly'higher than the preselected speed and atthis point the aforementioned control maintains the motor at constantpreselected speed in the manner described. This reverse-phase brakingaction will occur wherever the crank handle 35 is moved to a lower speedposition, or moved through zero speed position, or moved to a reversedspeed position, and is very effective to secure the desirable rapidchange from one speed condition to another.

Figure 2 illustrates an alternative arrangement ment of the system ofFig. l, and, in particular, a modified arrangement for operating theswitch I6, in which the springs 3|, 32 and the retarding torque device41, 48 of the arrangement of Fig. 1 are replaced by a different manualregulator involving an infinitely variable speed change device 50. Thepreferredform of device 50 includes the friction disc 5|, driven atconstant speed by a small self-starting synchronous motor 52 and engagedby a friction wheel 53, which is adjustable radially thereon to securevarious rates of rotation. Wheel 53 is fastened to gear 54, and by asuitable arrangement, they are free to turn as a unit on shaft 34 whichis fitted with the screw 36 threaded through the fixed plate 31, andwhich has the crank handle 35 as before. Wheel 53 and disc 5| are soarranged that it is necessary to move the wheel 53 entirely across thediameter of disc 5| by means of handle 35, in order to change from themaximum speed position in one direction of rotation of motor I0 to themaximum speed position in the other direction. Y

In operation of the modified arrangement of Fig. 2, self-startingsynchronous motor 52 drives friction disc 5| at constant speed and wheel53 is held againstdisc 5| by a constantpressure, rotating at a speed andin a direction determined by its distance from the center of the disc5|. For example, wheel 53 is stationary when it is at the center of disc5|, and will rotate increasingly 7 .faster as-it is moved toward theouter edge of the disc 5|. Also, wheel 53 will rotate in one directionwhen it is at one side of the center of the disc, and will rotate in theopposite direction when it is at the other side of the center. Themovement of wheel 53 is transmitted through gears 54 and 55 and shaft 56to the mechanical difierential 42, and toothed sector 28 will beactuated. through gears 40 and 4|,due to the difierence between theinputs to the mechanical difierential. Movement of sector 28 actuatesswitch l6 and the speed of the drive motor will then be controlled inthe manner previously described in connection with the arrangement ofFig. 1.

Where it is desired to control a direct current or series alternatingcurrent motor according to the system of this invention, the arrangementof Fig. 3 is employed. The armature 51, of the controlled motor ||l',such as a direct current motor,

is connected by shaft 58 to the mechanical dififerential 42', the shaft45' of which is either fitted with the flywheel 46 and retarding torquedevice '41, 48 of the arrangement of Fig, 1, as illustrated, Q

or is connected to the variable speed device 50 of the arrangement ofFig. 2. The motor l may have a series field winding 59 and the externalseries resistor 60 connected to one side of supply line 6|. Equalresistors 62 and 53 are connected across the armature 51, the mid-tapbetween them being connected to the series field 59 and to the fixedcontact 20" of the switch Fixed contacts 20' and 23 areconnectedtogether, as

are fixed contacts 22' and 2|, the latter being connected to line 6|Moving contacts i4 and ll of contactor l5 are connected across thearmature 51, and arc-suppressing condensers 24' and 25 are connectedacross the adjacent fixed and moving contacts of switch It.

In operation, in the arrangement of Fig. 3, the contacts first made whencrank handle 35' is set, namely, 14', 22' or H, 2|, will cause eitherresistor 62 or 58 to be placed in series with the armature 51, and theother resistor to be placed in 'parallel with the said seriescombination of the first resistor and the armature. This provides lowstarting torque as the first step, followed by full current supply uponclosure of contacts I1, 23' or contacts ll, 2|). Depending upon theautomatic speed control afforded by movement of 35 to the value as readon the corresponding pointer and dial 38, 38. This is so when the drivemotor In or III is at rest or running at any speed in either direction.By means or the mechanicaldiflerential 42 the drive motor will reach andhold this speed. In the arrangement of Fig.

'1, this is due to the relationship between the retarding torque of thedisc 41 and the restoring force or the two springs 3|, 32. The twoi'orces will seek tobe always equal and opposed to each other.

Although the speed of the drive motor may constantly change-aboutameanwhich is selected speed, the frequency of these changes will besufficiently high to provide, in effect, a predetermined constant speed.For a given load, the speed and acceleration of the controlled motor aregoverned entirely by the frequency of the intermittent contact action ofthe sensitive reversing and switching device, and by the ratio of thetime during which the contacts are made corn-- pared to the time duringwhich the contacts are broken. With the drive motor running at anypredetermined set speed, failure of the electric power service to themotor will cause it to slow down and come to rest. When the electricpower service is restored, the system will automatically cause the drivemotor to smoothly accelerate up to speed again, with no attention ormanual resetting being needed. 'I'his'system of 'speed con- ,trol isespecially desirable for obtaining low motor speeds.

While certain preferred embodiments of the invention have beenillustrated and described herein, it is to be understood that theinvention is not limited thereby, but is susceptible of changes in formand detail within the scope of the appended claims.

We claim:

1. In a control system for a reversible electric motor, the combinationof a source of power for the motor, a reversing switch directlyinterposed between said source and the motor and having opposite fixedcontacts and a movable contact interposed between them, means urgingsaid movable contact in engagement with.a fixed contact with apredeterminedforce, means controlled by said motor opposing said contactengagement force for disengaging said contacts, and means .acting onsaid urging means for transferring the tacts providing the reversingconnections to said source 01 power.

2. In a control system for an electric motor, the combination of asource of power for the motor, a reversing switch having normallyengaged movable and fixed contacts, said switch being directlyinterposed between said source and the motor, means responsive to speedof said motor, operative connections between said means and said movablecontact, whereby the engagement of said contacts is made and broken inaccordance with the speed changes of the motor, and means for shiftingthe engagement of said movable contact with another fixed contact toreverse the motor.

3. In a control system for a polyphase motor, the combination of asource of power, a switch interposed between said motor and saidsourceand having two sets of relatively movable cooperating contacts,direct connections between one set or contacts and certain phases ofsaid source, direct connections between said other set 0! con- .tactsand certain other phases of said source,

means for urging said sets of contacts successively in engagement, andmeans actuated by the motor opposing said urging means for controllingthe engagement and disengagement otsaid contact sets toregulate thespeed of rotation'otsaid motor.

ARTHUR P. Davis. enema sums.

